Hydraulic control apparatus for an automatic transmission of a vehicle

ABSTRACT

A hydraulic control apparatus for an automatic transmission accurately controls a variation in torque generated when a shift lever is turned from an N range into a D range or R range. The hydraulic control apparatus has a pressure governor for hydraulic pressure to be supplied from a spool valve to a clutch, by an actuator, thereby suppressing a variation in output torque of the automatic transmission. The hydraulic pressure governed by the actuator is introduced into the spool valve again, and it is supplied to a forward clutch and a reverse clutch through a hydraulic line switch for switching hydraulic lines communicated to the forward clutch and the reverse clutch from each other.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to an apparatus for controlling ahydraulic pressure used for speed change performed by an automatictransmission of an automobile, and particularly to a hydraulic controlapparatus for an automatic transmission which is intended to directlycontrol a hydraulic pressure to be supplied to a clutch on the basis ofan electric signal.

The control apparatus of this type has been known, for example, fromNissan's maintenance guide titled "Full Range Electronically ControlledAutomatic Transmission" issued by NISSAN MOTOR on March, 1987. In thiscontrol apparatus, an accumulator is disposed between a manual spoolvalve and a forward clutch and another accumulator is disposed betweenthe above spool valve and a reverse clutch. Another known hydrauliccontrol apparatus generates a variation in torque of an output shaft ofan automatic transmission when the position of a shift lever of anautomobile is changed between an N (Neutral) range and a D (Drive:forward) range or between the N range, and an R (Reverse) range isrelaxed by mechanically and electrically controlling a line pressureintroduced in the above spool valve. At the present time, the hydrauliccontrol apparatus having such a structure has been extensively used forautomobiles.

The above-described prior art hydraulic control apparatus, however, isdisadvantageous in that provision of two accumulators for forward andreverse clutches makes larger the size of a transmission using thecontrol apparatus, and that the accuracy of control for suppressing avariation in torque is deteriorated due to changes in mechanicalcomponents with time.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a hydraulic controlapparatus for an automatic transmission, which is improved in accuratelysuppressing a variation in torque generated when the position of a shiftlever of an automobile is changed between an N range and a D range orbetween the N range and an R range and in preventing the accuracy ofcontrol for suppressing a variation in torque from being deteriorateddue to changes of mechanical components with time, by adopting a controlsystem using a perfectly electronic circuit in place of a control systemusing a hydraulic circuit.

To achieve the above object, according to the present invention, thereis provided a hydraulic control apparatus for an automatic transmission,including: a means for generating a hydraulic pressure by driving ahydraulic pump using an engine drive force or an electric force; a spoolvalve automatically or manually driven by operation of a speed changelever; at least one clutch used for forward movement, reverse movementor speed change of a vehicle; a hydraulic control actuator for governinga hydraulic pressure applied to the clutch; and a control means forcontrolling the hydraulic control actuator; characterized by providing apressure governing means for governing a hydraulic pressure, which issupplied from the hydraulic pressure generating means to the clutchthrough the spool valve, by the hydraulic control actuator to suppress avariation in output torque of the automatic transmission. In the abovehydraulic control apparatus, preferably, the hydraulic pressure governedby the actuator is supplied to the forward clutch and the reverse clutchthrough a hydraulic line switching means for switching hydraulic linescommunicated to the forward clutch and the reverse clutch from eachother.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a schematic configuration of a hydrauliccontrol apparatus for an automatic transmission according to the presentinvention;

FIG. 2 is a typical view showing a principle of supplying a hydraulicpressure by a manual spool valve;

FIG. 3 is a view showing a configuration of a shift lever mechanismportion;

FIG. 4 is a correlation diagram showing a relationship between positionsof a shift lever and operational states of clutches;

FIG. 5 is a correlation diagram showing a relationship between hydraulicpressures upon N-R, N-D speed change and a torque To of an output shaftof the transmission;

FIG. 6 is a view showing the detailed configuration of the hydrauliccontrol apparatus shown in FIG. 1;

FIG. 7 is a view showing a schematic configuration of a hydrauliccontrol apparatus for a CVT; and

FIG. 8 is a correlation diagram showing a relationship between positionsof a shift lever and engagement of CVT clutches and supply of ahydraulic pressure to a pulley.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

FIG. 1 is a view showing a schematic configuration of a hydrauliccontrol apparatus for an automatic transmission according to oneembodiment of the present invention. In this embodiment, there is used afour-speed automatic transmission.

A transmission main body 1 includes an oil pump 2 for generating ahydraulic pressure; a reverse clutch (hereinafter, referred to as a"R/C") 3 turned on for reverse movement; a forward clutch (F/C) 4 turnedon for forward movement; a 2-4 clutch (2-4/C) 5 turned on for speedchange into a second and fourth speed; a high clutch (H/C) 6 turned onfor speed change into a third and fourth speed; and a lock-up clutch(L/C) 7. The turning on/off of these clutches changes a rotating ratioof a planetary gear (not shown) to carry out starting, reverse movement,or speed change, thereby allowing a vehicle to run desirably.

The transmission main body 1 is connected to a hydraulic controlapparatus 8 through an interface board 9. The use of the interface board9 reduces the production cost of the hydraulic control apparatus 8. Thereason for this is as follows. Even if design factors (the entire shapethereof, positions of portions for introducing a hydraulic pressures toclutches, and the like) of the transmission main body 1 are not matchedwith design factors (the arrangement of outlets of hydraulic lines) ofthe hydraulic control apparatus 8, the same hydraulic control apparatus8 can be matched with the transmission main body 1 by changing the shapeof the interface board 9 in accordance with the kind of the transmissionmain body 1.

The hydraulic control apparatus 8 includes a manual spool valve 10 and amanual spool valve chamber 11. It also includes hydraulic controlactuators 15, each of which is composed of a hydraulic control valve 12,a hydraulic control valve chamber 13, and an electromagnetic solenoid14. The electromagnetic solenoid 14 is driven by a transmissioncontroller 16 mounted on the hydraulic control apparatus 8. The numberof sets of the hydraulic control actuators 15 differs depending on thenumber of the clutches provided in the transmission main body 1. In theprior art apparatus, the number of mechanical control means correspondsto that of clutches; however, according to the present invention, onlyfour sets of the actuators may be provided for the four-speed automatictransmission.

The function of the hydraulic control apparatus 8 having the aboveconfiguration will be described in detail below. When a shift lever(which will be described later) of an automobile is operated, ahydraulic pressure generated by the oil pump 2 driven by an engine poweror an electric motor is introduced into the manual spool valve 10operated by manually or automatically from a pump pressure inputhydraulic line 23 (the hydraulic pressure is indicated by character A).In the case where the manual spool valve 10 is automatically operated,it is desired to be driven by an electromagnetic solenoid 14-e from theviewpoint of simplification of the structure of the shift lever andcontrol accuracy.

The hydraulic pressure thus introduced is outputted into each clutchsuch that the transmission is turned into a state indicated by each ofranges of parking (P), reverse (R), neutral (N), and forward or speedchange (D) on the basis of an operating position of the shift lever.

In this embodiment, it is important that, when the hydraulic pressure isintroduced from the manual spool valve 10 into a hydraulic control valve12-a for governing the hydraulic pressure applied to the R/C 3 and F/C4, the hydraulic pressure is returned again from an output hydraulicline 22 provided to the manual spool valve chamber 11 into the manualspool valve 10. With this configuration, the two clutches, R/C 3 and F/C4, can be controlled only by the hydraulic control actuator 15-a.

In this case, a hydraulic line switching means 17 for switchinghydraulic pressure introducing lines communicated to the two clutches,R/C 3 and F/C 4, from each other is required to be provided for themanual spool valve 10 and the manual spool valve chamber 11. Thehydraulic line switching means 17 includes the manual spool valve 10; aninput hydraulic line 18 for introducing a hydraulic pressure (indicatedby character C) from the hydraulic control valve 12-a into the manualspool valve 10; a hydraulic line 19 for supplying a hydraulic pressure(indicated by character D) from the input hydraulic line 18 into the F/C4; a hydraulic line 20 for supplying a hydraulic pressure (indicated bycharacter E) to the R/C 3; an output hydraulic line 22 for returningagain a hydraulic pressure (indicated by character B) into the manualspool valve 10; and the manual spool valve chamber 11 connected to thesehydraulic lines. The manual spool valve chamber 11 is also provided witha relief valve 21 for controlling the upper limit of the hydraulicpressure generated by the oil pump 2. The provision of the relief valve21 prevents an excessive rise in hydraulic pressure, thereby preventingbreakage of the hydraulic control apparatus 8.

The control of the hydraulic pressures applied to the R/C 3 and F/C 4 iscarried out for preventing a variation in torque of an output shaft ofthe transmission upon N-D, N-R speed change, thereby providing good ride(which will be described later with reference to FIG. 5). Such a controllogic is stored in a ROM (Read Only Memory, not shown) provided in thetransmission controller 16, and an N-D speed change switch and an N-Rspeed change switch (both, not shown) are provided on the shift leverfor controlling the hydraulic pressure using a signal supplied from eachof these switches as a trigger.

The hydraulic control apparatus 8 also includes a fail-safe mechanism.When the control system including the transmission controller 16 and theelectromagnetic solenoid 14 fails, the fail-safe mechanism allows theautomobile to run with the speed change ratio being fixed at the thirdspeed range. To fix the speed change ratio at the third speed range, thehydraulic pressures must be supplied to the F/C 4 and H/C 6 when asolenoid power supply is turned off. For this purpose, inelectromagnetic solenoids 14-a, 14-c, the arrangement of hydraulicpressure introducing lines 30-a, 30-c and drain lines 31-a, 31-c isreversed to the arrangement of hydraulic pressure introducing lines30-b, 30-d and drain lines 31-b, 31-d in the other electromagneticsolenoids 14-b, 14-d. In this case, there may be used theelectromagnetic solenoids 14-a to 14-d which have the same specificationin which the stroke becomes zero when the solenoid power supply isturned on. The electromagnetic solenoids 14-a to 14-d can be thusunified.

The purpose of fixing the speed change at the third speed range can beachieved not only by changing the hydraulic lines as described above butalso by the use of two kinds of electromagnetic solenoids 14-a, 14-c,and 14-b, 14-d which are reversed to each other in operationalcharacteristics, that is, different from each other in that the strokebecomes zero or it is maximized when the solenoid power supply is turnedon. Further, there is provided a function for supplying a hydraulicpressure from the hydraulic line 20 for the R/C 3 into a fail-safe valve34 and cutting-off the supply of a hydraulic pressure into the H/C 6upon reverse movement in the case where the control system is in thefailing state. As a result, the vehicle is allowed to run forward orreversely somewhat, for example, to a repair shop by operation of themanual spool valve 10.

FIG. 2 is a typical view showing a principle of supplying a hydraulicpressure by the manual spool valve 10.

In this figure, hydraulic pressure supplying states at ranges of parking(P), reverse (R), neutral (N), and forward or speed change (D) are shownfrom the upper side in this order.

In the parking range, a hydraulic pressure is introduced from the pumppressure input hydraulic line 23 into the manual spool valve chamber 11.When the introduced hydraulic pressure becomes excessively large, theabove-described relief valve 21 composed of a valve 24 and a spring 25is operated for controlling the introduced hydraulic pressure to be lessthan the maximum setting value. The maximum setting value is determinedon the basis of a previously selected biasing force of the spring 25.

In the reverse range, the manual spool valve 10 is moved leftward, sothat the hydraulic pressure supplied from the pump pressure inputhydraulic line 23 is outputted from the output hydraulic line 22. Thehydraulic pressure is introduced into the input hydraulic line 18through the hydraulic control valve 12-a. Then, the hydraulic pressuresupplied from the input hydraulic line 18 is outputted to the hydraulicline 20 communicated to the R/C 3 for controlling the R/C 3.

In the neutral range, the manual spool valve 10 is further movedleftward, so that the hydraulic pressure supplied from the pump pressureinput hydraulic line 23 is outputted from the output hydraulic line 22and is then introduced into the input hydraulic line 18 through thecontrol valve 12-a. However, since the hydraulic pressure in the inputhydraulic line 18 is cut-off by the manual spool valve 10, it is notintroduced to the clutch. At this time, the hydraulic pressure suppliedto the R/C 3 is discharged from the hydraulic line 20 through a drainline 26, with a result that the neutral state is established.

In the forward or speed change range, the manual spool valve 10 is movedrightward from the position in the neutral state, so that the hydraulicpressure supplied from the input hydraulic line 18 is outputted from thehydraulic line 19 communicated to the F/C 4 for controlling the F/C 4.In the case where the manual spool valve 10 in this state is moved intothe position in the neutral state, the hydraulic pressure supplied tothe F/C 4 is discharged from the hydraulic line 19 through a drain line27, with a result that the neutral state is established.

As described above, according to the present invention, the twoclutches, F/C 4 and R/C 3, can be controlled only by one manual spoolvalve 10. This is effective to reduce the size and cost of the controlapparatus. In the case where the hydraulic control actuator 15-a forcontrolling the F/C 4 and R/C 3 fails, a variation in torque upon N-D,N-R speed change is increased; however, the vehicle is allowed to runtemporarily, for example, to a repair shop by the hydraulic controlshown in FIG. 2.

FIG. 3 is a view showing a configuration of a shift lever mechanismportion. The shift lever mechanism portion functions to operate themanual spool valve 10 in the right and left direction as shown in FIG.2. It includes a shift lever composed of a shift knob 335, a lever 336,and a rotating shaft 337; and a connecting portion 338, a cam 339, apush rod 340, and a cam shaft 341, which are provided on the shiftlever.

When the shift knob 335 is moved in the right and left direction in FIG.3, the connecting portion 338 is turned around the rotating shaft 337and thereby the cam 339 is turned around the cam shaft 341. The cam 339has recesses which correspond to the P, N, R, and D ranges related tothe stroke of the manual spool valve 10. The position of the manualspool valve 10 is determined by fixing the position of the push rod 340in each of the recesses. In the case where the manual spool valve 10 iselectrically operated, a leading edge of the lever 336 is detected by aswitch 342 for checking each of the P, N, R, and D ranges; the signal issupplied to the transmission controller 16; and the electromagneticsolenoid 14-e is driven by the transmission controller 16, to therebycontrol the manual spool valve 10.

FIG. 4 is a correlation diagram showing a relationship between speedchange positions and operation of clutches. More specifically, there isshown a relationship between positions of the shift lever and engagementstates of the clutches. In this diagram, a round mark indicates a clutchengagement state, and a blank space indicates a clutch release state.Upon 1-2 speed change, while not shown, a torque applied to the clutchbecomes larger because of a large reduction ratio, with a result thatthe clutch is severely worn due to the excessive torque. In thisembodiment, to cope with such an inconvenience, a low one-way clutch(hereinafter, referred to as a "LO/C") is used. The LO/C is small insize and weight, and thereby it contributes to reduction in size andweight of the transmission. In the case where the LO/C is not used, oneset of hydraulic control actuator 15 used for controlling the clutchesmust be added.

Referring to FIG. 4, in the N and P ranges, all of the clutches areturned off, that is, in the release states. In the D range, at the firstspeed range, the F/C and LO/C are turned on, that is, in the engagementstates; at the second speed range, the F/C and 2-4/C are turned on; atthe third speed range, the F/C and H/C are turned on; and at the fourthspeed range, the H/C and 2-4/C are turned on. In the R range, the R/C isturned on.

FIG. 5 is a correlation diagram showing a relationship between hydraulicpressures upon N-R, N-D speed change and a torque To of an output shaftof the transmission. The torque To of the output shaft of thetransmission means an output torque of the output shaft of thetransmission main body 1. When the shift lever positional signal N, R orD representing a speed change range is inputted to the transmissioncontroller 16, the hydraulic control shown in FIG. 5 is carried out forcontrolling the torque To. The shift lever signal can be simply obtainedusing a switch for converting a position of the shift lever into anelectric signal. Such a switch is required for not only the case ofelectrically driving the manual spool valve 10 but also the case ofmanually driving the manual spool valve 10.

Referring to FIG. 5, when the position of the shift lever is changedbetween the N range and R range and between the N range and D range, theprior art apparatus shows characteristics indicated by broken lines.More specifically, in the prior art apparatus, a variation in torque Tobecomes large upon N-R, N-D speed change. This is because the prior artmechanical control system is difficult to perform fine control due to anaction accompanied by an inertia, so that there occurs a variation inpressure supplied to each of the R/C and F/c as indicated by the brokenline in FIG. 5. On the contrary, according to the present invention,since a pressure supplied to each of the R/C and F/C is electricallyfinely controlled as shown by a solid line in FIG. 5, the torque To hasa smooth characteristic, thus relaxing a uncomfortable feeling due tothe variation in torque.

FIG. 6 is a view showing the detailed configuration of the hydrauliccontrol apparatus 8 shown in FIG. 1. Here, there will be described theconfiguration intended to simplify the structure and reduce the cost ofthe hydraulic control apparatus 8. First, the manual spool valve 10 andthe manual spool valve chamber 11 are unified to form a casing as aspool valve unit 35; and the electromagnetic solenoid 14, the hydrauliccontrol valve 12, and the hydraulic control valve chamber 13 are unifiedto form each of control valve units 36, 37, 38, and 39. These units arethen assembled into the hydraulic control apparatus 8 for controllingthe transmission. In this case, the hydraulic control apparatus 8 can beeasily assembled at a low assembling cost by setting these units to beidentical to each other in terms of each of three (lateral,longitudinal, height) dimensions A, B, and C. Further, by use of theunits having the same shape, the production cost can be also reduced.

These units are assembled by stacking the units and fastening them toeach other using bolts 42, 43 passing through bolt holes 40, 41previously formed in the units and nuts 44, 45, 46, 47 screwed with bothends of the bolts 42, 43. Connecting portions of, for example, hydrauliclines 48, 49 between the adjacent ones of the units are airtightlysealed by seal rings 50, 51. The lateral width A of the control valveunits 36, 37, 38, 39 can be shortened by suitable arrangement of thehydraulic lines. In addition, the units may not identical to each otherin terms of all of the three dimensions A, B and C, but may be identicalto each other only in one or two of the three dimensions A, B, C.

The fail-safe function of the apparatus shown in FIG. 1 will be morefully described below. In FIG. 1, for reverse movement, when the manualspool valve 10 is moved to a position corresponding to the R range, ahydraulic pressure is supplied to the hydraulic line 20 for introducingthe hydraulic pressure to the R/C 3. At this time, the hydraulicpressure is also supplied to a hydraulic line 52 for introducing thehydraulic pressure to the H/C 6. The fail valve 34 shown in FIG. 1 isprovided for preventing such an inconvenience, and it is composed of ahydraulic valve 55 and a spring 56 in the control valve unit 37 in theconfiguration shown in FIG. 6.

The operation of the fail-safe valve 34 will be described. When thehydraulic pressure is supplied to the R/C 3, the hydraulic pressure issupplied to the lower side of the hydraulic valve 55 (see FIG. 6)through a hydraulic line 57, and the hydraulic valve 55 is moved upwardin FIG. 6, to discharge the hydraulic pressure supplied to the H/C 6 toa drain line 58. The hydraulic lines 52, 53, and 54 of the control valveunits 37, 38, and 39 intrduce the hydraulic pressure to the clutchesrespectively.

Each hydraulic line is formed into a straight shape, and a stopper forpreventing oil leakage is provided near the outer peripheral portionthereof. This contributes to reduction in production cost of thehydraulic control apparatus 8.

With this configuration, an inexpensive hydraulic control apparatushaving a fail-safe mechanism can be realized. Additionally, in the casewhere five speed change steps are required, one control unit which isthe same as the control valve unit 37 without the drain line 58 and thefail-safe valve 34 may be added to the configuration shown in FIG. 6, tothereby obtain a hydraulic control apparatus for five-speed change. Itis same way that one control unit which is the same as the control valveunit 36 without a hydraulic line 59 may be added to the configulation.

The present invention can be applied to a CVT (Continuously VariableTransmission). The CVT basically includes a tapered drive pulley forreceiving an engine drive force, a tapered driven pulley for outputtinga drive force to drive wheels, and a belt wound around the drive pulleyand the driven pulley, wherein the speed change is achieved by changinga ratio between diameters of the drive pulley and the driven pulleyaround which the belt is wound.

FIG. 7 is a view showing a schematic configuration of a hydrauliccontrol apparatus for a CVT.

Referring to FIG. 7, a transmission main body 60 includes an oil pump(hereinafter, referred to as an "O/P") 61 for generating a hydraulicpressure; a reverse clutch (R/C) 62 turned on for reverse movement; aforward clutch (F/C) 63 turned on for forward movement; a pulleypressure supplying portion (P/P) 64 for axially moving a pulley forspeed change; a line pressure generating portion (L/P) 65 for keeping ahigh accurate speed change ratio and managing a tension of a belt, and astarting clutch (S/C) 66 turned on for starting into forward or reversemovement. Also, there is provided a hydraulic control apparatus 67 forcontrolling hydraulic pressures used for operating these clutches. Thetransmission main body 60 is connected to the hydraulic controlapparatus 67 through an interface board 68. The use of the interfaceboard 68 reduces the production cost of the hydraulic control apparatus67. The reason for this is as follows. Even if design factors (theentire shape thereof, positions of portions for introducing a hydraulicpressures to clutches, and the like) of the transmission main body 60are not matched with design factors (the arrangement of outlets ofhydraulic lines) of the hydraulic control apparatus 67, the samehydraulic control apparatus 67 can be matched with the transmission mainbody 60 by changing the shape of the interface board 68 in accordancewith the kind of the transmission main body 60.

The hydraulic control apparatus 67 will be described in detail below.The hydraulic control apparatus 67 is similar in basic configuration tothe hydraulic control apparatus 8 shown in FIG. 1. A manual spool valve10 in this apparatus 67 is the same as that shown in FIG. 1, andtherefor, the explanation thereof is omitted. The hydraulic controlapparatus 67 is different from the hydraulic control apparatus 8 in theconfiguration of a control portion for a R/C 62 and a F/C 63. In thecase of the CVT, the control of the R/C and F/C for suppressing avariation in torque upon starting as shown in FIG. 5 is not required, sothat an electromagnetic solenoid is not used upon switching the R/C andF/C from each other by operation of the manual spool valve 10.Accordingly, the R/C and F/C can be switched from each other using aconfiguration that the hydraulic control actuator 15-a is omitted fromthe hydraulic control apparatus 8 shown in FIG. 1 and only stoppers 69,70 are provided. In this case, the control valve unit 36 shown in FIG. 6can be used, that is, the control valve unit for the four speedtransmission can be commonly used. This is effective to reduce thedesign and production costs.

Referring to FIG. 7, for operating the P/P 64, L/P 65 and S/C 66, ahydraulic pressure supplied from an output hydraulic line 22 is suppliedto hydraulic control actuators 71-b, 71-c, 71-d. The hydraulic pressurethus supplied is governed by electromagnetic solenoids 73-b, 73-c, 73-doperated on the basis of control signals supplied from a CVT controller72, to operate respective clutches, thereby realizing running and speedchange of the CVT.

The hydraulic control apparatus 67 also includes a fail-safe mechanism.When the control system including the CVT controller 72 and theelectromagnetic solenoid 73 fails, the fail-safe mechanism functions tofix the speed change ratio on a relatively small side (that is, speedincreasing side of the pulley) for allowing the automobile to runtemporarily, for example, to a repair shop. The setting is performedsuch that the case where the hydraulic pressure supplied to the P/P 64is large is taken as a speed decreasing side and the case where it issmall is taken as a speed increasing side. To fix the speed changeratio, it is required that when a solenoid power source is turned off,the supply of the hydraulic pressure to the P/P 64 is stopped and thehydraulic pressure is supplied to the L/P 65 and S/C 66. For thisreason, the control valve unit 38 is used for the P/P 64, and the basiccontrol valve unit 37 (not containing a fail-safe valve 34) is used forthe L/P 65 and S/C 66. In this case, electromagnetic solenoids 73 fordriving hydraulic control valves 12 can be configured to have the samespecification in which the stroke becomes zero when the solenoid powersupply is turned on.

FIG. 8 is a correlation diagram showing a relationship between positionsof a shift lever and engagement of CVT clutches and supply of ahydraulic pressure to a pulley. A round mark indicates a state in whicha hydraulic pressure is supplied, and a blank space indicates a state inwhich any hydraulic pressure is not supplied. In the N and P ranges,hydraulic pressures are supplied to the P/P and L/P in consideration ofresponsiveness upon starting; however, since the S/C is turned off, theautomobile does not start. In the D range, hydraulic pressures aresupplied to the F/C and S/C, to turn on the clutches, with a result thatthe automobile starts for forward movement. In this range, the rotatingratio between the two pulleys is changed to carry out speed change bycontrol of the hydraulic pressures supplied to the P/P and L/P. In the Rrange, a hydraulic pressure is not supplied to the F/C but is suppliedto the R/C, so that the automobile starts for reverse movement. Here,since the hydraulic pressures are also supplied to the P/P and L/P, thespeed change ratio upon reverse movement can be changed by control ofthe hydraulic pressures supplied to the P/P and the L/P.

As described above, according to the present invention, a hydrauliccontrol apparatus used for a steppedly variable transmission orcontinuously variable transmission can be simplified, so that it can beproduced at a low cost. Further, since a variation in torque upon N-D,N-R speed change can be suppressed, the operational ability of theautomobile can be improved. In addition, since the hydraulic controlapparatus includes a fail-safe function allowing the automobile to runto a repair shop when a control system fails, it becomes possible toenhance the safety.

What is claimed is:
 1. A hydraulic control apparatus for an automatictransmission, comprising:a speed change mechanism having a forwardclutch configured to be turned on when a speed change lever is shiftedfrom a neutral position to a forward position, and a reverse clutchconfigured to be turned on when the speed change lever is shifted fromthe neutral position to a reverse position; a spool valve configured tobe driven by operation of the speed change lever, and a spool valvechamber for the spool valve; a hydraulic control actuator arranged toadjust a hydraulic pressure generated by a hydraulic pump driven by anengine drive force or an electric force for controlling an engagementstate of said forward clutch or said reverse clutch of said speed changemechanism; and said spool valve chamber is provided with a supplyhydraulic line into which a hydraulic pressure is supplied from thehydraulic pump, an output hydraulic line for outputting the hydraulicpressure supplied from said introducing hydraulic line through saidspool valve, and an input hydraulic line for supplying again thehydraulic pressure from said output hydraulic line to said spool valve,whereby said forward clutch and said reverse clutch are controlled usingthe hydraulic pressure supplied to said input hydraulic line.
 2. Ahydraulic control apparatus for an automatic transmission according toclaim 1, wherein a hydraulic control valve is provided between saidoutput hydraulic line and said input hydraulic line of said spool valvechamber for adjusting the hydraulic pressure applied to said forwardclutch and said reverse clutch; andan electromagnetic solenoid isprovided to drive said hydraulic control valve.
 3. A hydraulic controlapparatus for an automatic transmission according to claim 2, wherein astopper for preventing oil leakage is provided in lieu of a valvechamber of said hydraulic control valve.
 4. A hydraulic controlapparatus for an automatic transmission according to claim 2, comprisinga spool valve unit composed of said spool valve and said spool valvechamber, and a control valve unit composed of said electromagneticsolenoid and said hydraulic control valve.
 5. A hydraulic controlapparatus for an automatic transmission according to claim 4, wherein aplurality of said control valve units are freely combined with eachother.
 6. A hydraulic control apparatus for an automatic transmissionaccording to claim 4, wherein said spool valve unit and said controlvalve unit, comprise casings identical to each other in at least twodimensions.
 7. A hydraulic control apparatus for an automatictransmission according to claim 4, wherein said spool valve is providedwith apparatus for switching said hydraulic lines from each other.
 8. Ahydraulic control apparatus for an automatic transmission according toclaim 1, wherein an electromagnetic solenoid is provided to drive saidspool valve.
 9. A hydraulic control apparatus for an automatictransmission according to claim 1, wherein said spool valve chamber isconfigured such that said input hydraulic line is positioned between ahydraulic line for supplying a hydraulic pressure to said forward clutchand a hydraulic line for supplying a hydraulic pressure to said reverseclutch.